1. Field of the Invention
The invention concerns a process for the production of pig iron with the help of fossil and secondary fuels, especially of hard and brown coal or of other organic fuels, such as refuse and sewage sludge, from iron ore or oxides which are made available in natural, pelleted form or in the form of ore dust or concentrate.
The invention can be used in the production of pig iron in blast furnaces or other installations which are suitable for a multi-stage carrying out of the process, such as e.g. the reduction of the ore to iron and the melting of the iron.
2. Description of Related Art
The carrying out of the process in the production of pig iron with the help of blast furnaces has, for many decades, remained substantially unchanged although a plurality of measures have become known for increasing the output by increase of the furnace dimensions and increasing of the process pressure and for the reduction of the coke consumption, e.g. by blowing in of other fuels, such as coal, heating oil, natural gas, coke oven gas, refuse, sewage sludge, ore, as well as the use of oxygen and the like. Results are given inter alia by Gudenau in the periodical xe2x80x9cStahl und Eisenxe2x80x9d 117 (1997), No. 6 under the title xe2x80x9cExperiments for the combined blowing in of coal dust and fine-grained iron-ore into the blast furnacexe2x80x9d and at the 1st TIMS/IEHK Metallurgical Symposium Sep. 28/29, 1997, in Cairo under the title xe2x80x9cEnvironmental and economical benefits by injecting iron containing recyclings and steel plant residues into the blast furnacexe2x80x9d and the VDI with the handbook xe2x80x9cUtilisation by smelting, secondary metal recovery and energy utilisation in the case of the thermal treatment of wastesxe2x80x9d at the seminar on the 22nd and Sep. 23rd, 1997, in Dxc3xcsseldorf.
A fundamental description of the blast furnace processes is given, inter alia, in the textbook of Ost, H: Rassow, B: xe2x80x9cTextbook of chemical technologyxe2x80x9d, 26th edition, Leipzig, Barth-Verlag, 1955.
Characteristic for the state of the art of the carrying out of the process in the blast furnace is the gasification of coke and of other organic fuels in countercurrent for the reduction of the iron ore so that the process heat requirement and the particular oxidation stage of the ore determine the gas composition and therewith the maximum possible fuel utilisation in the blast furnace which, referred to the oxidation potential of the fuel in practical operation, reaches approximately 75%. Therefore, indispensable component of the blast furnace process is the regenerative pre-heating of the process air which, outside of the blast furnace, uses a part of the chemical enthalpy of the blast furnace gas and thus returns into the process. Good blast furnace plant thus reach a fuel utilisation of about 83% in the case of the use of a high portion of expensive, scarce metallurgical coke as fuel.
In DE-OS 19 39 354 is described a coupling of a blast furnace or fan shaft furnace with an external reduction gas production, whereby blast furnace gas from the furnace is reacted with a gaseous, liquid or solid hydrocarbon preferably containing 1 to 13 carbon atoms in a tubular heater and/or heat exchanger with indirect heat supply. However, such an allotropic process possesses the disadvantage that the reaction temperature is limited to about 800 to maximum 950xc2x0 C. Thus, only a reduction gas can be obtained which has a relatively high proportion of CO2 and H2O and thus possesses a small reduction potential with regard to iron oxide. As a result, the furnace must be loaded with a large amount of gas which leads to a sacrifice of capacity. Furthermore, the CO2 contained in the reduction gas and the water vapour are reduced on the glowing coke in the blast furnace which also contributes to a reduction of the capacity of the furnace.
The relatively low reaction temperatures of up to maximum 950xc2x0 C. in the case of this allotropic reduction gas production process lies, however, below the melt temperatures of inorganic components such as are normally contained in qualitatively low value fuels, such as hard and brown coals, refuse or sewage sludge. It follows from this that this process is only suitable for very pure and thus expensive fuels.
In DE-AS 24 13 558, the external production of a reduction gas takes place with the help of a plasma burner, whereby the reaction enthalpy necessary for the gasification of the fuel must be supplied by electro-energy. Thus, this process is very expensive and can only be carried out when cheap electro-energy is available. In the process, recycled blastfurnace gas which contains CO, CO2, H2 and H2O and possibly carbon and/or hydrocarbon are ionised in an electric arc and brought into contact in a mixing chamber with a further part stream of blast furnace gas and carbon and/or hydrocarbon so that an endothermic post-reaction takes place. However, the process is also only suitable for very pure starting products, such as hydrocarbons or high-grade coal dust, since a slag removal is not possible not only from the combustion chamber but also from the mixing or reaction chamber of the reduction gas production.
Especially having regard to an ecologically-caused energy cost increase, for example by the introduction of an energy tax, the economy of this process is decreased and calls for other technical solutions for the reduction gas production, like the present invention.
From GB-PS 858 561, it is known to react solid fuels with air and/or oxygen to give a reduction gas, whereby the hot combustion products must be blown in at a temperature of about 1100 to 1600xc2x0 C. over a separate pipe system into a blast or fan shaft furnace. The technical carrying out of this process is very complicated and expensive. Furthermore, such process procedures in which the gases must be supplied at these high temperatures to the auxiliary nozzles have not proved themselves in practice. The high gas temperatures would require the construction of an external coal gasification directly on the blast furnace which, as is known, is practically not realisable because of the constructional actualities of the blast furnace plant.
The technical task and the object of the invention are, therefore, to suggest new possibilities for the better utilisation of the fuels, as well as for the further substitution of metallurgical coke by other qualitatively lower grade fuels, preferably by brown or hard coal, but also refuse and sewage sludge, as well as coke dust obtained in the case of reduction gas production, and for the increase of capacity of the blast furnace.
The task is solved by analysis of the decisive courses of the process of the iron ore reduction and iron smelting with the help of the thermodynamic system iron-carbon-hydrogen-oxygen.